Microelectronic devices (e.g. dies) are typically manufactured in large number on a semiconductor wafer. For various reasons, microelectronic devices may fail to perform correctly. Accordingly, as a part of the manufacturing process, various tests of the microelectronic devices are typically performed. Tests can include, for example, functional tests, speed tests and sorting, and burn-in testing. Testing is often performed at the wafer level (e.g., before the microelectronic devices are separated from each other in a process called singulation) to allow failed to devices to be identified before packaging the devices.
To perform tests on the wafer, temporary electrical connections to the microelectronic devices on the wafer are made. For example, the wafer can be placed into a prober, and the wafer brought into contact with a probe card assembly. The probe card assembly can include many probes that are arranged to make temporary pressure-based electrical contacts to corresponding terminals (e.g., aluminum bond pads) on the microelectronic devices. Alignment of the wafer and probe card assembly can be performed using optical systems. Testing can involve sending signals to and from the wafer through the probes.
Many factors make it challenging to ensure proper alignment between the probe card assembly and the wafer. For example, when the probe card assembly is installed in the prober, various alignment operations (e.g., tilt adjust) are performed to place the tips of the probes into parallel alignment with the surface of a stage on which the wafer will rest. When a probe card assembly is removed and reinstalled in a prober, it is typically necessary to go through the alignment process again.
Providing proper alignment is further complicated when temperature variations are present, as most materials change dimension as a function of temperature. A probe card assembly typically has a relatively large thermal mass (compared to the wafer), and thus it takes considerable time to change the temperature of the probe card assembly (e.g., when performing burn-in testing at elevated temperatures). During the time periods when the probe card assembly is being aligned, cooling down, or heating up, the prober is not being used to perform tests.